Erosion resistant materials find use in many applications wherein surfaces are subject to eroding forces. For example, refinery process vessel internals exposed to aggressive fluids containing hard solid particles such as catalyst particles in various chemical and petroleum environments are subject to both erosion and corrosion. The protection of these vessel internals against erosion and corrosion induced material degradation especially at high temperatures is a technological challenge. Refractory liners are used currently for components requiring protection against the most severe erosion and corrosion such as the inside walls of cyclones such as the internal cyclones in fluid catalytic cracking units (FCCU). The life span of these refractory liners is significantly limited by mechanical attrition of the liner, cracking and spallation. The state-of-the-art in erosion resistant materials is chemically bonded castable alumina refractories. These castable alumina refractories are applied to the surfaces in need of protection and upon heat curing harden and adhere to the surface via metal-anchors or metal-reinforcements. It also readily bonds to other refractory surfaces. The typical chemical composition of one commercially available refractory is 80.0% Al2O3, 7.2% SiO2, 1.0% Fe2O3, 4.8% MgO/CaO, 4.5% P2O5 in wt %.
Ceramic-metal composites are called cermets. Cermets of adequate chemical stability can provide an order of magnitude higher erosion resistance over refractory materials known in the art. Cermets are generally produced using powder metallurgy techniques where metal and ceramic powders are mixed, pressed and sintered at high temperatures. Since powder metallurgically produced cermets usually have homogeneous microstructure and uniform composition, sophisticated attachment methods are needed to attach cermets onto the metallic surfaces wherein erosion resistance of the surface is desired.
Composition gradient cermets are cermets wherein one surface of the cermet is ceramic-rich and the unexposed surface is metal-rich. In a typical composition gradient cermet there is a concentration gradient of the ceramic in the metal composition such that the concentration of the ceramic decreases with depth. These composition gradient cermets are desired and preferred for cost-effective attachment of cermets directly onto metal or alloy surfaces using methods such as welding due to the compatibility and ease of welding a substantially metallic object to another substantially metallic object. Furthermore, such composition gradient cermets can also exhibit superior durability particularly under conditions wherein thermal fluctuations are present. However, there is a need for effective processes to prepare composition gradient cermets.
One object of the present invention is to provide a process for preparation of cermets, particularly composition gradient cermets via reactive heat treatment of a metal alloy.
Another object of the present invention is to provide a composition gradient cermet product derived from the reactive heat treatment process.
These and other objects will become apparent from the description that follows.